If Bowser made a mess of your basket of onions from your vegetable garden, you should contact your veterinarian immediately. Onions -- Allium cepa -- can cause stomach problems or anemia.
Onions have a toxic component, N-propyl disulfide. After your pooch eats an onion, gastrointestinal problems may develop. He might start to drool or vomit. His mouth can become irritated. Of more concern, eating the onion can lead to red blood cell damage. The onion causes oxidation of red blood cells, forming Heinz bodies, which can cause the cell to rupture. If his red blood cells burst, Bowser can become anemic. You may notice him acting lethargic; if you look at his gums, you may notice they look pale rather than pink. Bowser’s urine may contain blood. On exam, your veterinarian may note that his heart rate and breathing rate are higher than normal as his system works harder to move oxygen around his body.
Treating Onion Toxicity
Your veterinarian may diagnose onion toxicity based on what you say she ate or may look for Heinz bodies on a blood sample. Treatment should be given immediately. Your veterinarian can induce vomiting to expel the material if Bowser recently ate the onions; he may administer activated charcoal to help prevent absorption of the toxins by the body. If Bowser is already showing signs of toxicity, he may need supportive care. Some pets need blood transfusions, while others need to be kept on IV fluids. Other dogs just need medical therapy to treat nausea.